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Warning!!
CHAPTER
THREE
Alkenes and
Alkynes
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3|1
Four models of ethylene:
(a) dash-wedge structure
Lycopene molecular structure
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Four models of ethylene:
(b) ball-and-stick structure
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Four models of ethylene:
(c) space-filling structure
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Unhybridized vs. sp2-hybridized
orbitals on carbon
Four models of ethylene:
(d) electrostatic potential diagram
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A trigonal carbon showing three sp2 hybrid
orbitals in a plane with a 120° between
them.
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The bonding in ethylene consists of one sp2-sp2
carbon-carbon σ bond, four sp2-s carbon-hydrogen σ
bonds, and one p-p π bond.
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Schematic formation of a
carbon-carbon double bond
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3 | 10
Rotation of one sp2 carbon 90° with respect to
another orients the p orbitals perpendicular to
one another so that no overlap (and therefore
no pi bond) is possible.
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3 | 12
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Electrostatic potential drawing of ethylene
showing accessibility of pi electrons (red)
to attack by electron-seeking reagents
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3 | 13
Eq. 3-2: geometric isomer ball-and-stick
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Eq. 3-2: geometric isomer ball-and-stick
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In the liver, ß-carotene is converted into
vitamin A first and then into 11-cis-retinal.
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Eq. 3-2: geometric isomer ball-and-stick
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Eq. 3-2: geometric isomer ball-and-stick
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Eq. 3-2: geometric isomer ball-and-stick
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Classification of reagents and alkenes by
symmetry with regard to addition reaction
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3 | 21
The addition of HBr to ethene; the
reaction equilibrium lies to the right
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3 | 23
Example 3.4 art
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3 | 20
Alkyl groups stabilize carbocations by donating
electron density from C--H and C--C sigma bonds
that can line up with the empty p orbital on the
positively charged carbon atom
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3 | 22
The formation of methyl radicals from
ethane; the reaction equilibrium
lies to the left
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3 | 24
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BASE GRAPH: Reaction energy diagram
for the addition of HBr to ethene
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BALL-AND-STICK MODEL OF
TRANSITION STATE 2: Reaction energy
diagram for the addition of HBr to ethene
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BALL-AND-STICK MODEL OF
REACTANTS: Reaction energy diagram for
the addition of HBr to ethene
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BALL-AND-STICK MODEL OF
TRANSITION STATE 1: Reaction energy
diagram for the addition of HBr to ethene
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3 | 26
BALL-AND-STICK MODEL OF
CARBOCATION INTERMEDIATE:
Reaction energy diagram for the addition
of HBr to ethene
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BALL-AND-STICK MODEL OF PRODUCT:
Reaction energy diagram for the
addition of HBr to ethene
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Reaction energy diagram for formation of
the isopropyl and propyl cations from
propene (Eq. 3.21)
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Art for equation 3.34: electrostatic
potential map
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3 | 32
Art for equation 3.34: comp-set art
structure
Art for equation 3.30
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Art for example 3.5
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Art for Equation 3.42
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Ethylene is central to the manufacture of
many industrial organic chemicals
Branched polyethylene
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3 | 37
Models of acetylene, showing its linearity.
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A triple bond consists of the end-on overlap of two sphybrid orbitals to form a σ bond and the lateral overlap
of the two sets of parallel oriented p orbitals to form
two mutually perpendicular π bonds
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3 | 41
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3 | 38
Unhybridized versus sp-hybridized
orbitals on carbon
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3 | 40
Electrostatic potential diagram of acetylene
showing the exposure of π electrons (red)
to attack by electrophiles
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